The present invention generally relates to focusing systems and image input apparatuses having a focusing system, and more particularly to an automatic focusing system and an image input apparatus which has such an automatic focusing system.
Apparatuses for transmitting images are realized by videophones and the like. However, an image input apparatus which is provided in such apparatuses generally does not have a high performance. In most cases, a pan focus camera having a focusing system is used as the image input apparatus. The image input apparatus having the focusing system is also used in video cameras.
Presently, a so-called mountain-climbing system is most popularly used as a system of obtaining focal information. The mountain-climbing system is proposed in "Automatic Focal Adjustment in Television Camera Using Mountain-Climbing Servo System", NHK Technical Report, Vol. 17, No. 1, pp. 7-12, 1965. According to this system, the focal information is obtained by use of an image signal which is output from an image pickup element. The existing focal system uses a bandpass filter to extract a high-frequency component which is included in the image signal, and the signal is generally processed in the analog form. In addition, a plurality of kinds of bandpass filters are used to exclude false information from the focal information. The use of the plurality of kinds of bandpass filters is proposed for example in a Japanese Laid-Open Patent Application No. 64-16177 and "New Automatic Focusing System", Television Society Technical Report.
On the other hand, there is a proposed electronic still camera which includes an image pickup element for subjecting the image into a photoelectric conversion, an analog-to-digital converter for converting an output image signal of the image pickup element into a digital image signal, and a memory for storing the output digital image signal of the analog-to-digital converter. The digital image signal is read out from the memory and a corresponding image is displayed on a television monitor or the like. Such an electronic still camera is proposed in Japanese Laid-Open Patent Applications No. 54-139422, No. 56-158583, No. 57-28480, No. 62-269581 and No. 63-146583.
The focal system of the image input apparatuses described above uses parts exclusively for the focal system, and the number of parts required in the focal system is large. In addition, because all signals are processed in the analog form, the accuracy of the focal system is poor. Moreover, the use of the plurality of kinds of bandpass filters also increases the number of parts required in the focal system.
On the other hand, the electronic still camera stores in the memory only the image signal which is obtained from the image pickup element. For this reason, it may take a long time to find an image picked up several years ago because the user must depend on his memory. In addition, there is no means of knowing who and when each image stored in the memory was actually taken.